Heretofore, as a gas container to store hydrogen or a compressed natural gas (CNG), from a viewpoint of lightening or the like, a container has been developed in which an inner shell is constituted of a resin liner and an outer peripheral surface of the resin liner is reinforced by a reinforcement layer (an outer shell) such as FRP or the like. As this type of resin liner, for example, a pair of bowl-like liner constituting members (substantially cylindrical members) are formed of a thermoplastic resin such as polyethylene beforehand, and end portions of this pair of liner constituting members are joined by heat plate welding (e.g., see JP 2004-211783 A (FIGS. 2 and 5)).